The case of a 68-year-old woman with lung adenocarcinoma complicated by apparently isolated widespread meningeal metastasis is described. Meningeal carcinomatosis is a rare complication of solid neoplasms. In fact, it occurs in less than 2% of lung carcinoma which is the most frequent cause of this syndrome. Although computed tomography and nuclear magnetic resonance may aid the diagnosis of this condition, only the cytological demonstration of neoplastic cells in the cerebrospinal fluid directly establishes it. In this patient, the onset of symptoms due to meningeal carcinomatosis complicated the course of a diagnosed lung adenocarcinoma with the acute onset of a confusional state and extended meningeal dissemination without clinical or instrumental findings of metastasis in other areas of the body. Acute confusional state is seldom the initial symptom of meningeal carcinomatosis. Nevertheless, in the neoplastic patient, this possibility must be taken into account after the most common causes of acute confusion have been excluded. Even when modern diagnostic imaging techniques are utilized, diagnosis must be confirmed by cytological examination of the cerebrospinal fluid.